1. Technical Field
The subject invention relates to a cylinder liner for a diesel engine of the type forming a combustion chamber in cooperation with a reciprocating piston, and more particularly to a diesel cylinder liner having a surface treatment designed to overcome the destructive effects of cavitation-induced erosion.
2. Related Art
Most heavy-duty diesel engines have wet sleeve cylinder liners which allow coolant to circulate on the outside of the cylinders to effectively dissipate heat. These wet sleeve liners are susceptible to a failure mechanism known as cavitation erosion.
Cavitation is a localized low-pressure zone that forms along the outer wall of a cylinder liner. It is caused by the flexing of the cylinder wall due to the high cylinder pressures experienced in diesel engine ignition. During combustion, the cylinder wall quickly expands and then returns to its original geometry. Cylinder wall expansion is more pronounced as the demand for power increases due to increased cylinder pressures. On a microscopic level, inward cylinder wall movement causes a low pressure zone to be created in the coolant adjacent to the cylinder wall. When the pressure zone drops below the vapor pressure point of the coolant, a vapor bubble is formed. When this low pressure zone returns to a high pressure zone, the vapor bubble collapses causing an implosion which results in pitting on the cylinder wall. This pitting, if left unchecked, can compromise the integrity of the cylinder liner.
One prior art attempt to prevent or reduce the phenomenon of cavitation and the resultant pitting, consists of formulating special coolants containing additives. Broadly, these additives fall into two categories: those based upon a borade or nitrite salt, and those formulated from an organic chemistry compound (carboxcylic/fatty acids). The former group works on the principle of reducing the surface tension of the coolant, which lowers the peak pressure reached within the bubble and provides for a “soft” implosion. The coolant solutions formulated from organic chemistry compounds also reduce surface tension, and in addition coat the liner's outer surface with a sacrificial layer of compounds which are continuously renewed by the chemistry make-up of the coolant.
Such specially formulated coolants, while moderately effective at controlling cavitation-induced erosion, are expensive and not always readily available. For example, if a service technician does not have a coolant with these special additives in ready supply, it is likely that any coolant and/or water will be used for the sake of expediency.
Accordingly, there is a need for an improved method of controlling cavitation-induced erosion which does not depend upon the availability of expensive, specially formulated coolants.
Another attempt to protect wet cylinder liners from cavitation-induced erosion operates on the principle of plating, or otherwise fortifying, the outer surface of the liner so that it is better able to withstand attack from imploding bubbles. For example, nickel and nickel-chromium electroplating have been used in the past. Other surface treatments and jacketing techniques have also been proposed to enable a liner to withstand cavitation erosion. These prior art strategies add substantial cost and complexity to the liner manufacturing operations. In many cases, they substantially increase the weight of the liner, or introduce some other ancillary negative effects. Accordingly, there is a need for alternative solutions to corrosion-induced erosion which do not significantly increase the expense of a diesel engine overhaul.